Child-directed speech in noise (Smith et al., 2024)

Purpose: Talkers adapt their speech according to the demands of their listeners and the communicative context, enhancing the properties of the signal (pitch, intensity) and/or properties of the code (enhancement of phonemic contrasts). This study asked how mothers adapt their child-directed speech (CDS) in ways that might serve the immediate goals of increasing intelligibility, as well as long-term goals of supporting speech and language development in their children.

Method: Mothers (N = 28) participated in a real-time interactive speech production/perception paradigm, in which mothers instructed their young (3- to 5-year-old) children, or an adult listener, to select the picture corresponding to a target word. The task was performed at low and high levels (56 vs. 75 dB SPL) of background noise to examine the Lombard effects of decreased audibility on speech production.

Results: Acoustic–phonetic analyses of CDS and adult-directed speech (ADS) productions of target words and carrier phrase (e.g., “Find pig”) revealed that mothers significantly enhanced the mean pitch, pitch variability, and intensity of target words in CDS, particularly at higher background noise levels and for younger children. Mothers produce CDS with a higher signal-to-noise ratio than ADS. However, limited evidence was found for phonetic enhancement of the segmental properties of speech. Although increased category separation was found in the voice onset time of stop consonants, decreased vowel category separation (an anti-enhancement effect) was observed in CDS.

Conclusions: Mothers readily enhance the suprasegmental signal properties of their speech in CDS, but not the acoustic–phonetic properties of phonemes. This study fails to provide evidence of phonetic enhancement in preschool children in a dyadic communication task under noisy listening conditions.

Supplemental Material S1. Model selection.

Supplemental Material S2. Mean pitch.

Supplemental Material S3. Pitch variability.

Supplemental Material S4. Intensity.

Supplemental Material S5. First formant (F₁) mean.

Supplemental Material S6. Second formant (F₂) mean.

Supplemental Material S7. First formant (F₁) variance.

Supplemental Material S8. Second formant (F₂) variance.

Supplemental Material S9. Vowel separation.

Supplemental Material S10. Prevoicing.

Supplemental Material S11. Voice-onset time (VOT) of voiced stops (/b/).

Supplemental Material S12. Voice-onset time (VOT) of voiceless stops (/p/).

Smith, N. A., Hammans, C. A., Vallier, T. J., & McMurray, B. (2024). Child-directed speech in noise: Testing signal- and code-based phonetic enhancement. Journal of Speech, Language, and Hearing Research, 67(1), 72–91. https://doi.org/10.1044/2023_JSLHR-23-00033